This invention relates to electrical feedthroughs, and, more particularly, for feedthrough pins utilized in the feedthroughs.
Many types of apparatus utilize an electrical feedthrough across a wall that separates two environments. The electrical feedthrough permits electrical signals and power to be conducted across the wall, but prevents any movement of mass, such as gas leakage, across the wall. As an example, an infrared sensor is typically contained in a vacuum enclosure. The sensor is cooled to cryogenic temperatures, typically about 77.degree. K. or less. Output signals are conducted from the sensor to electronic devices located exterior to the vacuum enclosure, without losing the hermetic vacuum seal, via an electrical feedthrough in the wall of the enclosure.
The feedthrough is usually constructed with a plurality of feedthrough pins hermetically sealed in bores in a feedthrough plate made of an insulating material such as a ceramic. The feedthrough plate is hermetically sealed to the remainder of the wall of the package structure, here the vacuum enclosure. The ceramic insulator electrically isolates the feedthrough pins from the wall and from each other.
An electrical connection is made to each end of the feedthrough pin. In order to achieve a reliable, uniform connection to the feedthrough pins by techniques such as wire bonding or tab bonding, the ends of the set of feedthrough pins should be closely coplanar. The ends of the feedthrough pins should also have a good quality, smooth surface finish. In order to achieve coplanar, smooth ends of the feedthrough pins, the ends may be lapped or otherwise processed after the feedthrough pins are fixed to the feedthrough plate.
It is difficult to achieve the required coplanarity and surface finish on the ends of the feedthrough pins at the operation which bonds the pins to the plate, using conventional techniques. There is therefore a need for an improved approach to achieving coplanar, bondable feedthrough pins, and the feedthrough construction. The present invention fulfills this need, and further provides related advantages.